EP1542238B1

EP1542238B1 - Aerosol particle charging equipment

Info

Publication number: EP1542238B1
Application number: EP03741432A
Authority: EP
Inventors: Kikuo 2-401 Hirodaigagara-Daiichishokuin- OKUYAMA; Manabu Shimada; Yosio Ohtani; Norikazu Namiki; Toshihiko Hino
Original assignee: Hamamatsu Photonics KK; Kanomax Japan Inc
Current assignee: Hamamatsu Photonics KK; Kanomax Japan Inc
Priority date: 2002-07-17
Filing date: 2003-07-16
Publication date: 2011-01-12
Anticipated expiration: 2023-07-16
Also published as: JP3910501B2; US7522703B2; EP1542238A1; KR20050028028A; AU2003281113A1; EP1542238A4; US20060108537A1; DE60335725D1; JP2004053298A; AU2003281113A8; KR100842851B1; WO2004008464A1

Abstract

Aerosol particle charging equipment, comprising an X-ray radiating part (22) radiating soft X-ray toward a chamber (21) and an inlet duct (23) and an outlet duct (24) installed on both sides of the chambers (21), wherein a radiated area is ionized by the soft X-ray, whereby the safe and easy-to-handle aerosol particle charging equipment can be provided.

Description

The present invention relates to a charging device of aerosol particles using an X-ray source for generating a soft X-ray.
Recent nanotechnology is given attention regarding nanophase material since the nanophase material has a property better than a conventional material. In the nanotechnology, manufacturing, generation, transportation, deposition, and measurement of nanoparticles are essential. Charging particles or obtaining an equilibrium charged state is an effective method for controlling the nanoparticles in transportation or deposition processes. For example, the nanotechnology is used in crystal film formation by electrostatic deposition of charged colloid nanoparticles, and synthesis of two component system nanoparticles by attachment of nanosize aerosols each charged to opposite polarities. Charging of nanoparticles is indispensable in measurement of nanoparticles using static electricity such as, nanocluster DMA and particle beam mass analyzer.
Particles are normally charged as a result of impact between the gas ion and the particles. The charging state of the particles can be divided into unipolar charge and bipolar charge in accordance with the charged state. A bipolar charging device using radiation is usually used. A radiation source includes radioactive substances such as americium (²⁴¹Am), krypton (⁸⁵Kr), polonium (²¹⁰Po) and the like.
Fig. 1 is a cross sectional view showing one example of a conventional bipolar charging device using radiation. In Fig. 1, an inlet duct 2 for introducing aerosols, and a outlet duct 3 for exhausting the aerosols are provided on both ends of a cylindrical chamber 1. A radiation source 4 such as americium (²⁴¹Am) is arranged at an intermediate part of the chamber 1. Rectifying plates 5, 6 for rectifying the aerosols passing through the chamber are arranged on the left and the right. The rectifying plates 5, 6 include a plurality of fine openings, are used for rectifying the aerosols, and are arranged in the vicinity of the inlet duct 2 and the outlet duct 3, as shown in the figure. By arranging the radiation source 4 within the chamber 1 and introducing the aerosols into the chamber 1, the fine particles of the aerosols are charged by a large amount of positive and negative ions, and the equilibrium charging state can be obtained when the average charged amount is substantially zero.
Further, a charging device for generating unipolar charged ions is recently given attention for its wide range of applications. The conventional unipolar charging device, as shown in Fig. 2, includes a chamber 11 configured with a cylindrical part 12 made of resin for side surfaces, and with electrodes 13, 14 for upper and lower surfaces thereof. Voltage is applied between the upper and lower electrodes 13, 14 from a high voltage power source 15, and an ammeter 16 for measuring minute current is connected therebetween. A radiation source 17 of americium (²⁴¹Am) is arranged on the electrode 14 at the lower surface of the chamber 11. If the height of the chamber is for example, 90 mm, α ray only reaches to about 40 mm due to its range; thus, bipolar ions are generated at the lower part of the chamber. As an electric field is generated, ions of desired polarity move towards the upper part of the chamber 1. Therefore, when aerosols are flowed through the inlet duct 18, the unipolar particles are discharged from the outlet duct 19, thereby achieving unipolar charging.
The charging device using corona discharge is capable of generating unipolar or bipolar high concentration ions, and is thus widely used. According to this method, when direct current or alternating current voltage of high voltage is applied to the electrode, unipolar or bipolar ions can be generated in the vicinity of the electrode.
However, in the conventional device for charging the aerosol particles using radiation, the half-life of the radioactive substance is long and thus has a problem in terms of safety. For example, americium requires 432.2 years, and krypton (⁸⁵Kr) requires 10.72 years. Thus, management over a long period time is difficult. Further, polonium (²¹⁰Po) has a short half-life of 138 days, and thus has a problem in that the line source must be changed every few months.
Further, the conventional unipolar charging device using radiation has small generation number of ions, and has losses inside the charging device or inside a piping, and thus has a disadvantage of being difficult to use unipolar charged nanoparticles for various applications. It also has a disadvantage in that a charging operation can not be stopped when necessary.
Additionally, the charging device using corona discharge generates ozone, causes corrosion of electrodes during discharge, and generates particulate substances by the gas phase reaction at a strong electrical magnetic field, and thus has a disadvantage of polluting air. The corona discharge also has a disadvantage of generating current noise.
In the device according to US 4,701,941 , the generation of X-radiation occurs when a powder is subjected to electro-dispersion in an evacuated chamber. The powder is of a conducting or semiconducting material, and is supported on the lower of two electrodes in the chamber. When the chamber pressure is about 10-5 Torr or lower, and a high voltage is applied across the electrodes, part of the powder forms a dispersed particulate cloud in the space between the electrodes. The dispersion of the powder results in the generation of X-radiation which is transmitted through the wall of the chamber or through a window in the apparatus. Visible light is produced if a phosphor is included in the chamber, and is irradiated by X-rays generated upon dispersion of the powder, or if the powder includes particles of a phosphor.
According to EP 1070960 , the ionization chamber comprises a non-radioactive ionization source, a reaction partial chamber, a feed for introducing an analyte to the reaction partial chamber, and a line for removing the analyte. The ionization chamber comprises a non-radioactive ionization source, a reaction partial chamber, a feed for introducing an analyte to the reaction partial chamber, and a line for removing the analyte. The positive pole of a beam potential is connected to an X-ray anode in an evacuated partial chamber so that an X-ray beam produced in the anode hits a separating wall which is impermeable to electrons but permeable to the electron beam produced in the anode. An electrode is arranged in the reaction partial chamber to produce photoelectrons in a conversion layer. The separating wall is made of beryllium and has a thickness of 10-200 µm, or is made of mica and has a thickness of 7-40 µm. The ionization chamber comprises a non-radioactive ionization source (10), a reaction partial chamber, a feed for introducing an analyte to the reaction partial chamber, and a line for removing the analyte. The ionization chamber comprises a non-radioactive ionization source, a reaction partial chamber, a feed for introducing an analyte to the reaction partial chamber, and a line for removing the analyte. The positive pole of a beam potential is connected to an X-ray anode in an evacuated partial chamber so that an X-ray beam produced in the anode hits a separating wall which is impermeable to electrons but permeable to the electron beam produced in the anode. An electrode is arranged in the reaction partial chamber to produce photoelectrons in a conversion layer.; Preferred Material: The separating wall is made of beryllium and has a thickness of 10-200 µm, or is made of mica and has a thickness of 7-40 µm.
The purpose of JP 8299786 A is to provide a photocatalytic reactor capable of efficiently decomposing and removing the contaminant, malodorous matter, suspended fungi, etc., in a gas. For this purpose, the reactor consists of a reaction vessel having a gas inlet and a means to irradiate a gas introduced into the vessel from the inlet with X-rays and is further provided with a means to generate an electric field in the vessel and filters arranged in the electric field and irradiated with the X-rays from the means. The gas introduced into the vessel is irradiated directly with X-rays, and consequently the gaseous contaminant and suspended fungi in the gas are efficiently ionized or charged. The ionized contaminant and charged fungi are attracted toward the photocatalyst by the electrical attractive force of the electric field in the vessel, efficiently adsorbed on the photocatalyst, decomposed and sterilized by the photocatalysis and removed.
It is the object of the invention to provide a charging device of aerosol particles that is safe and easy to handle.
This object is achieved by the aerosol particle charging device of claim 1, claim 2 characterizing a preferred embodiment of the invention.
According to a first aspect of the present invention, a aerosol particle charging device comprises a chamber, an inlet duct which flows gas including aerosol particles to be processed into the chamber, a outlet duct which exhausts the processed aerosols from the chamber, and an X-ray emitting section which is arranged facing the chamber and emits an X-ray having a main wavelength within a range of 0.13 nm to 2 nm.
In this aerosol particle charging device, the X-ray emitting section may include a power switch for controlling emission and stop of the X-ray.

Brief Description of Drawings

Fig. 1 is a cross sectional view showing one example of a conventional bipolar charging device of aerosol particles.
Fig. 2 is a cross sectional view showing a configuration of a conventional unipolar charging device of aerosol particles.
Fig. 3 is a cross sectional view showing an entire configuration of an aerosol particle charging device according to the present invention.
Fig. 4 is a graph showing change in a charging ratio with respect to a particle diameter.
Fig. 5 is a graph showing particle retention time and charged particle number concentration of this embodiment.

Fig. 3 is a cross sectional view showing a configuration of a charging device of aerosol particles according to the present invention. In the figure, a chamber 21 is a brass cylindrical container having an inner diameter dl of 40 mm. An X-ray emitting section 22 is arranged at an opening at a side of the chamber 21. The X-ray emitting section 22 emits X-rays from the middle of a left end of the cylindrical chamber. An inlet duct 23 for introducing the aerosols is arranged at an upper part of the chamber 21. A outlet duct 24 for exhausting the bipolar charged aerosols is arranged at the middle of the other end of the chamber. A rectifying plate 25 having a plurality of openings for rectification is arranged in the vicinity of the outlet duct 24. Here, a distance from the X-ray emitting section 22 to the rectifying plate 25 is 90 mm.
The X-ray emitting section 22 is an X-ray source for generating a soft X-ray of 0.13 to 2 nm, and emits the X-ray at a solid angle of 120° from a window made of beryllium. Such X-ray emitting section is disclosed in, for example, Japanese Patent No. 2951477 . The ions are generated across the entire emission range on a steady basis by the emission of the X-ray. If the numbers of positive and negative ions generated at the same time are unbalanced, unbalance also occurs in the charged state of the particles by one of the ions. However, according to the X-ray emitting section used in the present invention, an equivalent amount of positive and negative ions are simultaneously generated since weak X-ray is constantly irradiated. Therefore, the aerosols are neutralized without unbalance in the charging polarity. Further, ozone, electromagnetic noise, powder dust or the like does not occur. The X-ray emitting section 22 includes a power switch 22a. Emission and stop of the X-ray can be controlled by turning the power switch 22a on and off.
An operation result of the aerosol particle charging device of this invention will now be explained using the drawings. Fig. 4 shows a ratio of the particles of relatively low concentration each having an aerosol diameter of 10 nm, 20 nm and 30 nm charged while retained in a region irradiated by the X-ray. In the figure, ▲ is a charging ratio of when a retention time is 3.2 seconds and Δ is when a retention time is 0.5, seconds in this embodiment. Moreover, ● is a case where a retention time is 3.2 seconds, and ○ is of when it is 0.5 seconds in the conventional charging device using americium as the radiation source. As seen from the figure, a charging phenomenon of the charging device using the X-ray source is a charging process similar to the conventional device using the radiation source.
Fig. 5 shows the number concentration of charged particles with respect to time retained in the chamber. A solid line is for the aerosol particle charging device using the soft X-ray according to this invention, and a broken line is for the conventional charging device using americium as the radiation source. A curve A is when a particle diameter is 30 nm, curve B is when a particle diameter is 50 nm, and curve C is when a particle diameter is 100 nm. As shown in the figure, in the charging device using the X-ray source, the particle number concentration reaches a peak at around 1.2 seconds regardless of the particle diameter. On the other hand, in the charging device using americium, the peak is at around 2.6 seconds. Therefore, the particles can be charged within a time shorter than the conventional device. Thus, the retention time of the particles in the chamber becomes short, and a sufficient charging can be performed to a flow of large flow rate.
The present invention is thus easy to handle and generate ions at a high concentration compared to the conventional charging device using radiation source or corona discharge. Further, bipolar ions are simultaneously generated, and thus aerosols can be neutralized.
If the power switch is arranged at the X-ray emitting section, switching can be easily performed by turning the power switch on and off, and thus has effects of being able to stop the generation of X-rays during non-operation, or to check the difference of the charging effect. For example, during an emergency or in a time of disaster of when using or storing the charging device, the radiation source may be exposed thereby causing external or internal explosion in the worst case of an emergency, disaster and the like in the charging device using the radiation source, but in the present device, safety is ensured due to a current break (automatic circuit including power switch or electric power failure). That is, safety can be ensured in handling and storage, and the X-ray can be irradiated only when necessary.

Claims

An aerosol particle charging device comprising:
a chamber (21) having a first and a second end;

an inlet duct (23) which is configured to introduce a gas flow including aerosol particles to be processed into said chamber (21);

an outlet duct (24) which is configured to exhaust the gas flow including processed aerosol particles from said chamber (21); and

an X-ray emitting section (22),

said X-ray emitting section (22) facing said chamber (21), is arranged in the middle of the first end of the chamber (21) and emits an X-ray of wavelength within a range of 0.13 nm to 2 nm,

characterized in that

a rectifying plate (25) is arranged in the vicinity of said outlet duct (24) and has a plurality of openings for rectifying the gas flow introduced into said chamber (21).
The device according to claim 1, wherein said X-ray emitting section (22) includes a power switch which is configured to control emission and stop of the X-ray.